Btw: my father has this too, he is an ISFp, he is really amazingly good at doing geometric calculation in hi shead. He once showed me this problem he solved where you see a 3D object from only a few given angles, and you are supposed to fill in the missing parts to complete the geometric shape (Almost like a visual logic, because sometimes if you don't have enough info you have to say that it could be like this or that). I think synesthesia is linked to a form of giftedness and is a useful tool for specific kinds of problems.